github.com/aykevl/tinygo@v0.5.0/src/machine/machine_atmega.go

// +build avr,atmega

package machine

import (
	"device/avr"
)

// Configure sets the pin to input or output.
func (p GPIO) Configure(config GPIOConfig) {
	if config.Mode == GPIO_OUTPUT { // set output bit
		if p.Pin < 8 {
			*avr.DDRD |= 1 << p.Pin
		} else {
			*avr.DDRB |= 1 << (p.Pin - 8)
		}
	} else { // configure input: clear output bit
		if p.Pin < 8 {
			*avr.DDRD &^= 1 << p.Pin
		} else {
			*avr.DDRB &^= 1 << (p.Pin - 8)
		}
	}
}

// Get returns the current value of a GPIO pin.
func (p GPIO) Get() bool {
	if p.Pin < 8 {
		val := *avr.PIND & (1 << p.Pin)
		return (val > 0)
	} else {
		val := *avr.PINB & (1 << (p.Pin - 8))
		return (val > 0)
	}
}

func (p GPIO) getPortMask() (*avr.RegValue, uint8) {
	if p.Pin < 8 {
		return avr.PORTD, 1 << p.Pin
	} else {
		return avr.PORTB, 1 << (p.Pin - 8)
	}
}

// InitPWM initializes the registers needed for PWM.
func InitPWM() {
	// use waveform generation
	*avr.TCCR0A |= avr.TCCR0A_WGM00

	// set timer 0 prescale factor to 64
	*avr.TCCR0B |= avr.TCCR0B_CS01 | avr.TCCR0B_CS00

	// set timer 1 prescale factor to 64
	*avr.TCCR1B |= avr.TCCR1B_CS11

	// put timer 1 in 8-bit phase correct pwm mode
	*avr.TCCR1A |= avr.TCCR1A_WGM10

	// set timer 2 prescale factor to 64
	*avr.TCCR2B |= avr.TCCR2B_CS22

	// configure timer 2 for phase correct pwm (8-bit)
	*avr.TCCR2A |= avr.TCCR2A_WGM20
}

// Configure configures a PWM pin for output.
func (pwm PWM) Configure() {
	if pwm.Pin < 8 {
		*avr.DDRD |= 1 << pwm.Pin
	} else {
		*avr.DDRB |= 1 << (pwm.Pin - 8)
	}
}

// Set turns on the duty cycle for a PWM pin using the provided value. On the AVR this is normally a
// 8-bit value ranging from 0 to 255.
func (pwm PWM) Set(value uint16) {
	value8 := value >> 8
	switch pwm.Pin {
	case 3:
		// connect pwm to pin on timer 2, channel B
		*avr.TCCR2A |= avr.TCCR2A_COM2B1
		*avr.OCR2B = avr.RegValue(value8) // set pwm duty
	case 5:
		// connect pwm to pin on timer 0, channel B
		*avr.TCCR0A |= avr.TCCR0A_COM0B1
		*avr.OCR0B = avr.RegValue(value8) // set pwm duty
	case 6:
		// connect pwm to pin on timer 0, channel A
		*avr.TCCR0A |= avr.TCCR0A_COM0A1
		*avr.OCR0A = avr.RegValue(value8) // set pwm duty
	case 9:
		// connect pwm to pin on timer 1, channel A
		*avr.TCCR1A |= avr.TCCR1A_COM1A1
		// this is a 16-bit value, but we only currently allow the low order bits to be set
		*avr.OCR1AL = avr.RegValue(value8) // set pwm duty
	case 10:
		// connect pwm to pin on timer 1, channel B
		*avr.TCCR1A |= avr.TCCR1A_COM1B1
		// this is a 16-bit value, but we only currently allow the low order bits to be set
		*avr.OCR1BL = avr.RegValue(value8) // set pwm duty
	case 11:
		// connect pwm to pin on timer 2, channel A
		*avr.TCCR2A |= avr.TCCR2A_COM2A1
		*avr.OCR2A = avr.RegValue(value8) // set pwm duty
	default:
		panic("Invalid PWM pin")
	}
}

// I2CConfig is used to store config info for I2C.
type I2CConfig struct {
	Frequency uint32
}

// Configure is intended to setup the I2C interface.
func (i2c I2C) Configure(config I2CConfig) {
	// Default I2C bus speed is 100 kHz.
	if config.Frequency == 0 {
		config.Frequency = TWI_FREQ_100KHZ
	}

	// Activate internal pullups for twi.
	*avr.PORTC |= (avr.DIDR0_ADC4D | avr.DIDR0_ADC5D)

	// Initialize twi prescaler and bit rate.
	*avr.TWSR |= (avr.TWSR_TWPS0 | avr.TWSR_TWPS1)

	// twi bit rate formula from atmega128 manual pg. 204:
	// SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR))
	// NOTE: TWBR should be 10 or higher for master mode.
	// It is 72 for a 16mhz board with 100kHz TWI
	*avr.TWBR = avr.RegValue(((CPU_FREQUENCY / config.Frequency) - 16) / 2)

	// Enable twi module.
	*avr.TWCR = avr.TWCR_TWEN
}

// Tx does a single I2C transaction at the specified address.
// It clocks out the given address, writes the bytes in w, reads back len(r)
// bytes and stores them in r, and generates a stop condition on the bus.
func (i2c I2C) Tx(addr uint16, w, r []byte) error {
	if len(w) != 0 {
		i2c.start(uint8(addr), true) // start transmission for writing
		for _, b := range w {
			i2c.writeByte(b)
		}
	}
	if len(r) != 0 {
		i2c.start(uint8(addr), false) // re-start transmission for reading
		for i := range r {            // read each char
			r[i] = i2c.readByte()
		}
	}
	if len(w) != 0 || len(r) != 0 {
		// Stop the transmission after it has been started.
		i2c.stop()
	}
	return nil
}

// start starts an I2C communication session.
func (i2c I2C) start(address uint8, write bool) {
	// Clear TWI interrupt flag, put start condition on SDA, and enable TWI.
	*avr.TWCR = (avr.TWCR_TWINT | avr.TWCR_TWSTA | avr.TWCR_TWEN)

	// Wait till start condition is transmitted.
	for (*avr.TWCR & avr.TWCR_TWINT) == 0 {
	}

	// Write 7-bit shifted peripheral address.
	address <<= 1
	if !write {
		address |= 1 // set read flag
	}
	i2c.writeByte(address)
}

// stop ends an I2C communication session.
func (i2c I2C) stop() {
	// Send stop condition.
	*avr.TWCR = (avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWSTO)

	// Wait for stop condition to be executed on bus.
	for (*avr.TWCR & avr.TWCR_TWSTO) == 0 {
	}
}

// writeByte writes a single byte to the I2C bus.
func (i2c I2C) writeByte(data byte) {
	// Write data to register.
	*avr.TWDR = avr.RegValue(data)

	// Clear TWI interrupt flag and enable TWI.
	*avr.TWCR = (avr.TWCR_TWEN | avr.TWCR_TWINT)

	// Wait till data is transmitted.
	for (*avr.TWCR & avr.TWCR_TWINT) == 0 {
	}
}

// readByte reads a single byte from the I2C bus.
func (i2c I2C) readByte() byte {
	// Clear TWI interrupt flag and enable TWI.
	*avr.TWCR = (avr.TWCR_TWEN | avr.TWCR_TWINT | avr.TWCR_TWEA)

	// Wait till read request is transmitted.
	for (*avr.TWCR & avr.TWCR_TWINT) == 0 {
	}

	return byte(*avr.TWDR)
}

// UART on the AVR.
type UART struct {
	Buffer *RingBuffer
}

// Configure the UART on the AVR. Defaults to 9600 baud on Arduino.
func (uart UART) Configure(config UARTConfig) {
	if config.BaudRate == 0 {
		config.BaudRate = 9600
	}

	// Set baud rate based on prescale formula from
	// https://www.microchip.com/webdoc/AVRLibcReferenceManual/FAQ_1faq_wrong_baud_rate.html
	// ((F_CPU + UART_BAUD_RATE * 8L) / (UART_BAUD_RATE * 16L) - 1)
	ps := ((CPU_FREQUENCY+config.BaudRate*8)/(config.BaudRate*16) - 1)
	*avr.UBRR0H = avr.RegValue(ps >> 8)
	*avr.UBRR0L = avr.RegValue(ps & 0xff)

	// enable RX, TX and RX interrupt
	*avr.UCSR0B = avr.UCSR0B_RXEN0 | avr.UCSR0B_TXEN0 | avr.UCSR0B_RXCIE0

	// 8-bits data
	*avr.UCSR0C = avr.UCSR0C_UCSZ01 | avr.UCSR0C_UCSZ00
}

// WriteByte writes a byte of data to the UART.
func (uart UART) WriteByte(c byte) error {
	// Wait until UART buffer is not busy.
	for (*avr.UCSR0A & avr.UCSR0A_UDRE0) == 0 {
	}
	*avr.UDR0 = avr.RegValue(c) // send char
	return nil
}

//go:interrupt USART_RX_vect
func handleUSART_RX() {
	// Read register to clear it.
	data := *avr.UDR0

	// Ensure no error.
	if (*avr.UCSR0A & (avr.UCSR0A_FE0 | avr.UCSR0A_DOR0 | avr.UCSR0A_UPE0)) == 0 {
		// Put data from UDR register into buffer.
		UART0.Receive(byte(data))
	}
}